Transcript for Women Testify About Alleged Affairs With Man Accused of Killing Wife

suburban seattle man on trial for murdering his wife, more than seven years after her death. New testimony in court from women who say he cheated on his wife with them. And the police interview tapes just revealed to jurors, where he seemed to directly contradict them. Abc's neal karlinsky has that story for us. Reporter: One after the other, they took the stand right in front of him. Women who say they were intimate with a married david pietz. The man accused of killing his wife, nicole, and who police say portrayed himself as a loving husband. Yeah. I remember kissing him. We had sex. Reporter: A co-worker testified, pietz began their relationship back when he was engaged. I asked him why he was getting married. And he said that at that point, it was too late to back out of it. Reporter: Nicole pietz, david's wife, vanished in 2006. Her body was later found in a wooded area, strangled. Now, seven years later, pietz is on trial, charged by prosecutors who say he killed his wife because he was unhappy with their marriage. The detectives built a case on circumstantial evidence and dna. A woman pietz met at a gym said he twice slipped the drug ecstasy into his wife's drinks. He told me he would put it in her red bull. Trying to loosen her up to get her to do a threesome. Reporter: Jurors heard something different from david pietz himself. An audio recording of his interview with police, in which he said he never used drugs and had virtually no sex drive. I don't have much of a l libido. It's kind of an opposite of what the stereotype is. Reporter: He is calm in the interview. And said he feared his wife may have overdosed on medication. He has pleaded not guilty and continued to deny involvement in his death. A trial that will play out for the next month and a half. For "good morning america," neal karlins karlinsky, abc news, seattle. Let's get more from dan abrams. Seven years after the fact. And we have the prosecution, many have a smoking gun here. They have to put together a puzzle for jurors of little pieces. Remember, they didn't charge him until they were able to use some new technology to be able to move this case forward, only recently. So, they're going to want to begin -- this is how they're starting, talking about motive. They want to warm the jurors up to the idea of convicting this guy. Why would he have wanted to do this? Here are the reasons why. Warming the jurors. Heating them up. That testimony catches your ear. It's salacious and it's sexual. But there's an important relevance to it. He had said something about his own libido, which completely contradicts what these women are saying. He's telling the police, in essence, one thing. And then, they're bringing these witnesses to say, that's not at all what was the case. A lie in a police investigation is much more important than just the idea that, oh, he was having an affair. They're trying to fill out more of the contradictions with some dna evidence they do have. That's right. They begin the process by putting the jurors in the mood to convict, which is to say, here's why. They don't have to prove motive. But they want to. And they feel that they can here because actually, the motive evidence, where they are now, to some degree is stronger than some of the other evidence in connection with this case. Dan abrams, thanks very much.

This transcript has been automatically generated and may not be 100% accurate.

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